Theory Research On All-metal Aromaticity Sandwich Species:[Sb_nAu_nSb_n]~m(n=3,4,5,6;m=-3,-2,-1,-2)

The size of the cluster is between the atom and the macroscopic system,and its microscopic structure and the amazing physical chemical properties open up a new way for the creation and development of the new material.Therefore,the cluster quickly became the object of study in the experiment and theory.The calculation of the three-dimensional structure,bonding properties and stability of cluster are helpful for future experimental research and provide some theoretical basis.In 2015,Sun Zhongming group synthesis the first cases of all metal sandwich aromatic compounds,[Sb3Au3Sb3]3-,the compound is composed of three layers of metal surface.It looks like a three triangular prism structure,cyclo-Au3 is located in the middle of two cyclo-Sb3 triangle.The results show that[Sb3Au3Sb3]3-has a wide band gap(3.08eV),that is,the whole metal system may exhibit semiconductor properties.It is important that the system has the characteristics both of all metal sandwich compounds and all metal aromatic compounds.All-metal sandwich compounds and all-metal aromaticity are new concepts in the field of cluster chemistry.Therefore,this research has great significance in the field of metal aromaticity and coordination chemistry.Based on the synthesis of[Sb3Au3Sb3]3-in experiment,this paper predicted other all-metal aromaticity sandwich species[SbnAunSbn]m(n=3,4,5,6;m=-3,-2,-1,-2)through density functional theory(DFT)and Gauss 09 package.Its geometric structure were screened and optimized.And its bonding properties,orbital interaction,stability,potential application were calculated and analyzed.The main conclusions are as follows:Optimization results show that the[SbnAunSbn]m(n=3,4,5,6;m=-3,-2,-1,-2)have good characteristics of aperture size,the aperture size are 1.64 A,2.88 A,3.73 A,4.80 A,respectively.And its symmetry is as follows:D3h,D4h,C2v,C2h.Frequency calculation shows that all systems have positive frequency,so these structures are located at the local minimum of the potential energy surface.Bonding analysis showed that Sb-Sb is 2c-2e non-polar σ bond,which is composed of the p orbital of two Sb atoms.The Au-Sb is the 2c-2e polar σ bond,which is composed of the p orbital and s orbital of Au atom.In addition,there are aurophilic-interaction in Au-Au bond in[SbnAunSbn]m(n=3,4,5,6;m=-3,-2,-1,-2).The bond distance of Au-Au is decreased gradually with the expansion of ring,so the interaction between Au and Au atom is increased gradually.The results of stability studies show that the bond energy of Sb-Au is very strong in the title species.And the dissociation reaction of these compounds is a spontaneous endothermic process because the changes of enthalpy(AH)and Gibbs free energy(△G)are significantly positive.And the ionization potential demonstrates that these compounds do not easy to lose electrons.The large Egap of title species indicate that it can maintain its structural characteristics and chemical characteristics in the process of clusters self-assembly.In addition,the large Egap also indicates that these compounds have potential applications in semiconductor materials.Aromaticity studies show that[SbnAunSbn]m(n=3,4,6,m=-3,-2,-1,-2)have multiple aromaticity,including:a aromaticity,π aromaticity and δ aromaticity,and also have tubular aromaticity.In[SbnAunSbn]m(n=4,5,6;m=-2,-1,-2)the stability depends mainly on the cyclo-Aun(n=4,5,6),because the cyclo-Aun NICS(0.0)and NICS(1.0)than cyclo-Sbn NICS(0.0)and NICS(1.0).In[Sb3Au3Sb3]3-,its stability depends on cyclo-Sb3.In addition,the mechanical stability studies show that these compounds have good mechanical stability.The analysis of potential application indicate that the Sb site is the favorable for absorbing CO in the title species,which reason is that the Sb sites are more prone to nucleophilic reaction.Further adsorption energy calculations show only the adsorption energy of[Sb3Au3Sb3]3-is negative,indicating that the adsorption reaction is an exothermic reaction between[Sb3Au3Sb3]3-and CO.The adsorption of other species are positive,indicating that the adsorption of CO will lead to the energy of whole system increases,it is not conducive to the stability of the system.Even if the CO was adsorbed on the surface of the compound,it may also fall off naturally.The density of state analysis also shows that the strong interaction between CO and[Sb3Au3Sb3]3-though the p-p orbitals interaction.Hence,[Sb3Au3Sb3]3-is more suitable than others to serve as the CO adsorption.